Receiver which tunes by adjusting magnetic core antenna



June 12, 1956 F. c. BREWSTER RECEIVER WHICH TUNES BY ADJUSTING MAGNETIC CORE ANTENNA Filed Nov 20, 1951 INVENTOR.

Franklin 0. Brewster nited taes Application November 21), 1951, Serial No. 257,375

2. Qiaims. (Cl. 25ii-2l5) The present invention relates to improvements in radio receivers and more particularly to an improved antenna system and tuner for radio receivers of the type having a self-contained antenna.

The present practice in radio receiver design and construction is to provide a self-contained antenna for use on the broadcast band within the frequency range of 550 to 1600 kilocycles. The self-container antenna is usually of the loop type and for tuning the loop, a tuning capacitor of the variable condenser type may be employed. Such variable condensers are among the more expensive components used in the construction of a radio receiver and include a relatively large amount of critical material.

An alternative manner of providing the variable tuned circuits for a radio receiver has been to use a permeability tuned coil shunted by a fixed condenser thus avoiding the use of a variable tuning condenser. Permeability tuning units generally comprise a cylindrical coil having an axially movable ferromagnetic core for purposes of varying the permeability of the medium within the coil and hence the coil inductance. When such permeability tuned coils are used in superheterodyne receiver circuits it has been necessary to provide separate antennas inas much as the permeability tuned coil did not provide in itself sufiicient pickup.

It is therefore an object of the present invention to provide a radio receiver with an improved form of selfcontained antenna system.

Another object of the present invention is to provide permeability tuned antenna for use in a self-contained radio receiver antenna system.

Yet another object of the present invention is to provide a simple and inexpensive combined antenna and tuner for a radio receiver.

A feature of the present invention resides in the provision of a coil and a ferromagnetic core for tuning the same for use in a combined antenna pickup and tuned radio frequency circuit, with the coil being so arranged that radiated signals picked up by the movable ferromagnetic core are coupled to the coil to reinforce the signals directly picked up by the coil regardless of the tuning position of the core Within the coil.

The permeability tuned antenna and tuned circuit coil of the present invention may be used to advantage in superheterodyne circuits also employing a permeabiilty tuned oscillator coil, and a feature of the present invention resides in the horizontal positioning of the tuned antenna coil together with the vertical positioning of the tuned oscillator coil to increase antenna signal pickup by the antenna coil and likewise minimize antenna signal pickup and interaction by the oscillator coil. It should be noted that most broadcasting stations employ horizontally polarized transmitting antennas.

Another feature of the permeability tuned antenna system of the present invention, when used in a superheterodyne receiver circuit, is in the provision of the tracking and mechanical drive arrangement whereby simultaneous movement of the ferromagnetic tuning cores of both the antenna and oscillator coils, provides properly related frequency changes in the two circuits.

Further objects, features, and the attending advantages of the present invention will be apparent upon consideration of the following specification and drawings, in which:

Fig. 1 is a front elevational view partly broken away of a superheterodyne radio receiver embodying the antenna system of the invention;

Fig. 2 is an end section of the receiver on the line 2-2 of Fig. 1.

Fig. 3 is a schematic diagram of the permeability tuned antenna circuit of the invention; and

Fig. 4 is a diagrammatic representation of the permeability tuned antenna coil used with a permeability tune'd oscillator coil in a superheterodyne circuit.

In practicing the invention there is provided a radio receiver of the superheterodyne type having permeability tuned antenna and oscillator circuits. The permeability tuned antenna circuit is so constructed and positioned that signals picked up by the inductor including the coil and core thereof are adequate for radio reception. It has been learned that a high permeability ferromagnetic core has the property of collecting antenna signals which may be coupled therefrom into a coil. According to the present invention the permeability tuned radio frequency coil is provided with an additional, spaced, and series connected winding of closely wound turns positioned on the end of the coil form to surround the ferromagnetic core in its position farthest removed from the tunable Winding of the coil. Thus for all tuning positions of the ferromagnetic core the antenna signal picked up by the core is coupled into the tuned circuit to reinforce the antenna signals directly picked up by the coil. The core is made longer than is necessary for tuning the coil to provide additional signal pickup. In order to provide tracking of the permeability tuned antenna coil with the oscillator coil of the superheterodyne receiver, it may be necessary to vary the turn spacing along the lengths of the tuned portion of the coil.

Referring to Figs. 1 and 2 of the drawings, a radio re ceiver embodying the invention is shown, including a receiver cabinet 10 formed of plastic or other nonconducting material. The cabinet 10 may enclose a standard radio receiving chassis 11, having mounted thereon tubes 12 and coils 13 which are diagrammatically shown inasmuch as they are not directly at part of the present invention. The position of a loudspeaker 14 is also shown in dotted line outline on Fig. 1. The tunable circuits of the radio receiver and the tuned antenna system of the present invention are mounted in the front of the receiver cabinet and in front of the radio receiver chassis. Although the invention is to be described in connection with a superheterodyne type of radio receiver it should be understood that the combined tuned antenna and radio frequency coil of the present invention may be used in any form of radio receiver such as a tuned radio frequency receiver.

Fastened at the front of the radio receiver cabinet is a vertically positioned plate 15, pref rably of insulating material, on which the antenna and oscillator coils are mounted together with the tuning dial mechanism to be further described. The permeability tuned antenna coil i6 is mounted in a horizontal position by means of the angle bracket 17 and rubber grommet 18 which permits some flexible movement or deviation of the antenna coil from the exact horizontal position as shown by the dotted lines of Fig. 1. Similarly the oscillator coil 19 is vertically positioned by means of the bracket 20 and rubber grommet 21. The variably tuned coils 16 and 19 are provided with high permeability ferromagnetic cores 22 and 23 respectively which are pivotally connected at 24 and 25 to a bell crank lever 26. It should be pointed out that the ferromagnetic cores do not necessarily have the same permeability. Details of the mechanical connections are shown in Fig. 4 and it will be seen that both of the cores 22 and 23 are capable of individual adjustment by means of the threaded connections 26 and 27.

Instead of mounting the oscillator coil 19 in a vertical position, it may be mounted horizontally and provided with a suitable electrostatic shield to prevent interaction with the antenna coil. In such case the mechanical connections to the movable cores would be suitably modified to accommodate the change in coil positions.

It will be apparent that angular movement of the bell crank lever 26 will cause simultaneous axial movement of the ferromagnetic cores 22 and 23 within their respective antenna and oscillator coils 16 and 19. A tuning dial knob 30 is connected to drive shaft 31 for rotating the pulley 32 and dial cord 33 connected to drive the drum 34 and angularly rotate the bell crank 26 which is secured to the drum 34. The rubber grommets 18 and 21 provide limited flexibility in the mounting of the antenna and oscillator coils which is required as the bell crank 26 is rotated to reciprocate the ferromagnetic cores within the coils. The connections 26 and 27 permitting the individual adjustment of the relative positions of the iron cores 22 and 23 within their respective coil provide for the initial alignment of the coils in the receiver circuits as is well understood.

Referring to Fi 3 of the drawings, there is illustrated in detail the circuit of the permeability tuned antenna coil of the present invention, as it may be applied to a radio receiver. It will be seen that the antenna coil tuned circuit 16 is comprised of the series connected coil winding portions 40, 41 and the fixed condenser 42 connected in parallel therewith. The high permeability ferromagnetic tuning sing or core 22 is adapted to be moved axially within the coil and the arrangement of the winding portions 40 and 41 is such that the core is movable through the portion 41, and into and out of the portion 40. Thus the iron core 22 is at all times enclosed within the winding portion 41 which is spaced from the winding portion 40. The portion 49 may be referred to as the tuned or tunable portion of the coil and movement of the core 22 with respect to this portion causes tuning of the receiver through the broadcast band from 550 to 1600 kilocycles as mentioned above. On the other hand, the portion 41, which may include a large number of closely wound turns, functions primarily as a coupling coil for the antenna signals picked up by the ferromagnetic core.

The free end of the antenna signal coupling winding portion 41 may be connected to the receiver ground 43 while the free end of the tunable winding portion 40 may be connected to an input terminal of the receiver such as the control grid 44 of the electron tube (not fully shown) in the first stage of a receiver. If desired, the coil connections may be reversed from that shown.

The combined tuned antenna and radio frequency circuit of Fig. 3 is diagrammatically shown in Fig. 4 of the drawings together with a superheterodyne mixer oscillator tube 45 and a superheterodyne oscillator coil 19 also of the permeability tuned type. The fixed capacitor 47 is connected in parallel with the permeability tuned oscillator coil 19. Various circuit elements connected to the electrodes of the mixer tube 45 have been omitted from the drawing for the sake of clarity inasmuch as such elements and their connections are well known in the art and do not form a part of the present invention. For example, the oscillator coil feedback loop may be as shown at 28 altho it will be understood that any suitable form of os cillator and feedback arrangements may be used. As mentioned before the tunable winding portion 40 of the antenna coil, when used in a superheterodyne circuit, may be formed with variable turn spacing along its length in ill) order to secure the necessary tracking of the antenna coil with the superheterodyne oscillator coil.

Systems as disclosed have been found to provide highly satisfactory signal pickup. It is to be pointed out that both the tuning and coupling portions of the coil provide pickup as well as the tuning core. The core may have a length greater than is necessary for tuning to provide increased signal pickup and also so that a part of the core is always within the coupling portion of the coil.

In the foregoing, a novel form of self-contained permeability tuned antenna system for a radio receiver has been described. While the antenna system has been particularly described in connection with a superheterodyne receiver it should be understood that the principles of the present invention may be applied equally as well to other forms of radio receivers. It is apparent that various modifications may be made without departing from the spirit of the invention and intended scope of the appended claims.

I claim:

1. A tunable radio frequency antenna structure for a radio receiver including a single inductor for picking up received waves and for selecting the received waves, said inductor comprising a helically wound coil portion and a high permeability core portion mounted for movement within said coil portion, said coil portion and said core portion constituting the sole means of the radio receiver for picking up radio frequency signals from the air, said coil portion and said core portion of said inductor also constituting the sole tuning means of the antenna structure, said coil portion having first and second axially positioned winding sections connected in series, said core portion being movable from a first position wherein said core portion extends within said first and second winding sections for tuning said coil portion to a first frequency, to a second position in which said core portion extends only within said second winding section for thereby tuning said coil portion to a second frequency having a value at least twice that of said first frequency, with the positions of said core portion between said first and second positions thereof tuning said coil portion to frequencies within the range defined by said first and second frequencies, said core portion having a length greater than that required for tuning said coil portion to said first frequency so that increased pickup of radio frequency signals is provided thereby, said antenna structure including fixed means for supporting said coil portion and means for providing movement of said core portion within said coil portion.

2. A superheterodyne radio receiver having a self contained tuned antenna system including in combination, a cabinet, a single inductor for picking up received waves and for selecting the received waves including, an elongated helicaily wound coil mounted in a horizontal position in said cabinet, and a first high permeability core mounted for movement within said coil for changing the inductance thereof, a condenser connected across said coil and forming therewith a tuned antenna input circuit, said coil and said core constituting the sole means of the receiver for picking up radio frequency signals from the air, said coil and said core of said inductor also constituting the sole means for tuning said antenna input circuit, said coil having a first tuning portion and a second cou pling portion, with said coil portions being spaced and axially positioned and connected in series, said core being movable from a first position wherein said core extends within said first and second Winding portions to tune said antenna input circuit to a first frequency to a second position in which said core extends only within said second winding portion to thereby tune said antenna input circuit to a second frequency, said core having a length greater than that required for tuning said input circuit to said first frequency so that increased pickup of radio frequency signals is provided thereby, an oscillator circuit including a vertically mounted coil and a fixed condenser, and a second high permeability core mounted for movement within said coil of said oscillator circuit, said second core being movable between first and second positions for changing the tuning of said oscillator circuit, and tuning means for simultaneously moving said first and second cores, with the positions of said first and second cores between said first and second positions thereof tuning said antenna and oscillator circuits respectively through a range of frequencies, the winding pitch of said tuning portion of said radio frequency coil being so related to the winding pitch of said coil of said oscillator circuit that simultaneous movement of said first and second cores by said tuning means produces the same frequency changes in said antenna and oscillator circuits, said tuning means including a rotatable drive shaft and a bell crank connected to said drive shaft, and means connecting the respective ends of said bell crank to said first core and to said second core to move said cores axially upon rotation of said drive shaft.

References Cited in the file of this patent UNITED STATES PATENTS 2,095,420 Polydoroif Oct. 12, 1937 2,190,048 Sinninger Feb. 13, 1940 2,259,250 Jacob Oct. 14, 1941 2,363,101 Van Der Heem Nov. 21, 1944 2,424,506 Sands July 22, 1947 2,489,114 Vladimir Nov. 22, 1949 2,525,438 Wuerfel Oct. 10, 1950 2,555,475 Dewhurst June 5, 1951 2,555,511 Sands June 5, 1951 2,565,261 Wen Yuan Pan Aug. 21, 1951 2,581,348 Bailey Jan. 8, 1952 

